Technical Field
The disclosure is directed to a sensing apparatus and more particularly, to a motion detection device using radio frequency (RF) waves.
Description of Related Art
With development of technologies, various portable electronic apparatuses and wearable electronic apparatuses have been vigorously developed. For wearing comfort and portable convenience, the portable electronic apparatuses and the wearable electronic apparatuses are developed toward being compact-size, which causes difficulty and inconvenience to the finger touch operations. Therefore, in order to allow users to operate the portable electronic apparatuses and the wearable electronic apparatuses more intuitively and conveniently, a concept that a human is a controller has become one of the major study researches in recent years. By means of movements of body extremities, a user can operate an electronic product equipped with a three-dimensional motion sensing technique more intuitively and conveniently. Currently available applications of the motion sensing techniques include a contact type (such as data glove systems and electromyography (EMG) control apparatuses) and a non-contact type (such as non-contact image recognition systems and Doppler radars), which can provide various body motion sensing methods for human-computer interaction interfaces.
A Doppler radar utilizes electromagnetic waves for sensing, which is provided with high sensibility and sensing capability for crossing obstacles, and thus, becomes highly anticipated. In year 2013, Fadel Adib et al. from Massachusetts Institute of Technology (MIT) proposed a Wi-Fi system using a Wi-Fi signal with a known frequency and modulation scheme as a radar transmission source, which is operated with an Inverse Synthetic aperture radar (ISAR) technique for tracking a moving target object after walls. However, this system has low resolution for recognizing motions of the target object, which causes difficulty to the application in short-distance gesture detection. In addition, Qifan Pu et al. from University of Washington proposed a WiSee system utilizing a specific Wi-Fi signal for gesture sensing. In this WiSee system, each sub-channel in a signal has to be modulated for transmitting a mass of information with continuity by means of orthogonal frequency-division multiplexing (OFDM) to improve signal spectral resolution, such that a Doppler frequency shift induced by a hand motion cam be detected. Apparently, the aforementioned methods requires modulated signals which are specifically processed for the motion sensing, which cause limitations to application environments. Besides, all currently available spatial gesture sensing systems have insufficient sensibility for detecting human physiological parameters, such as respiration, heart rates.